Multiplex pulse repetition rate remote control system



April 26, 1960 s w. LICHTMAN MULTIPLEX PULSE REPETITION RATE REMOTE CONTROL SYSTEM Filed April 8, 1952 R.F. 115:5 CARR, AMPLIFIER OSCILLATOR I l suPER- GATHODE HETERODYNE FoLLowER R EIv R CHANNEL 3 E 2% 6 I-I 2 K E I I X/ f l VIDEO PULSE 7 VARIABLE AMPLIFIER GENERATOR DELAY .coMBINER L 26\ I CHANNEL 2/ I PULSE EQ- HT2 I 8 T2--| sTRETcI-IER 3 5 I S r ILII ILIIL UL E R GENERATOR e, 'QE COMBINER CHANNEL I T N0.3 3- I 3-I Low PAss KEYER [I n 4 I I FILTER r |LLH [L11 ?;E I:II F'Ii$oR VARIABLE-COMBINER I I DELAY T 4 cIIANNELNQIj' CHANNELNQZ QFIANNELNQEIj FILTER FILTER FILTER WW 6W WW?- II II II .1523 IF II II GI 62 T 7| 12 T 63 AUDIO AUDIO AUDIO AMPLIFIER AMPLIFIER AMPLIFIER I REcTIFIER REcTIFIER REcTIFIER I I I 0.0. 0.0. 0.0. AMPLIFIER AMPLIFIER AMPLIFIER I I I I INVENTOR uTILIzATIoN UTILIZATION UTILIZATION SAMUEL w. LICHTMAN DEVICE N0.l DEVICE No.2 DEVICENO.3

ATTORNEYJ United States Patent MULTIPLEX PULSE REPETITION RATE REMOTE CONTROL SYSTEM Samuel W. Lichtman, Ox'on Hill, Md.

Application April 8, 1952, Serial No. 281,253

8 Claims. (Cl. 343-228) (Granted under Title 35, U.S. Code (1952), see. 266) This invention relates to remote control radio systems, and more particularly to a radio control system for controlling operations ata station remote from a control station, such as an inaccessible location, or a mobile vehicle.

Familiar to the prior art are remote control radio systems wherein command intelligence is transmitted from acontrol station to a remote station in the form of a particular frequency of modulation of a carrier wave signal. In systems of this type operation of a plurality of respective controls or functions at the remote station isachieved by varying the modulation frequency of the carrier to different respective selected values.

The present invention is an improvement over systems of the general type above described, and provides a mula tiple control channel system whereby several difierent operations or functions at a remote station can be controlled simultaneously. Control signals are used which enable the transmission of command intelligence for controlling each of several discrete operations at the remote station simultaneously, without confusion or destructive interference of the intelligence at the remote station. Moreover provision is made by this invention for proportional control of the various controlled operations at the remote station. That is, the degree of response at the remote station of any one operation or function can be varied smoothly from zero to maximum in proportion tona selected setting at the control station of the control device for that operation.

It is an object of this invention therefore to provide a' multi-channel remote control radio system wherein a plurality of discrete operations at a remote station can be controlled simultaneously from a control station.

It is another object to provide a multichannel remote control system wherein a plurality of modulation intelligence signals can be transmitted concurrently withbut garbling or destructive interference of the intelligence at the receiver.

' It is another object to provide a remote control system wherein the degree of response of a controlled operation at a remote stationis proportional to a selected setting of a control device at the controlling station.

These and other objects and features of the present invention will appear more fully hereinafter from the following detailed description considered in connection with the accompanying drawings which disclose one embodiment of the invention. It is expressly understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention, for which reference should -be had to the appendedclaims.

I In the drawings, wherein like reference characters refer to like elements in all the figures:

Figure 1 is a block diagram of the transmission portion of a radio remote control system constructed in accordance with this invention.

Figure 2 is a block diagram of a portion of a receiving system constructed in accordance with the invention.

2,934,760 Patented Apr. 26, 1960 "ice Figure 3 is a block diagram of the remainder of a receiving system constructed in accordance with the invention.

Briefly stated this invention contemplates a multi-channel remote control system wherein the command intelligence or control signals for the various channels take the form of audio frequency pulse modulation of a common carrier frequency signal, with a different pulse repetition rate distinguishing each respective control channel. Control of several discrete operations at the remote station simultaneously is obtained by modulating the transmitted carrier wave signal simultaneously with pulses at the several different repetition rates representing the respective control channels. Upon demodulation of the carrier in the receiver at the remote control station, the pulses at the several different pulse repetition rates are separated by suitable filters for subsequent selective control of the different respective remote operations. The different pulse repetition rates used to control the diiferent remote operations are chosen in such a manner as to minimize signal coupling and interference between channels and between modulation harmonics. Smooth proportional control of the degree of response in any one channel is achieved by splitting each pulse of the pulse modulation for that channel into at least two individual pulses. By varying the time phase relationship of these individual pulses of the control signal, the precision of recurrence of pulses distinguishing a particular channel can be compromised to produce an amplitude variation in the response of the filter circuit for that particular channel at the remote station receiver.

s A radio control system constructed in accordance with my invention will now be described in detail. Turning to Figure 1 there is shown the control station or transmission portion of such a system. A carrier frequency signal is generated by power oscillator 1. The various control channel modulation signals are produced by selectively instituting operation by the several audio frequency pulse generators 2, 3, and 4, which operate at different selected pulse repetition rates.

To achieve smooth proportional control of the response for each channel at the remote station receiver, means is provided in the transmission portion of the system to compromise the precise periodicity of the pulses produced by any one pulse generator 2, 3, or 4. The circuits for compromising the periodicity of the output of the several pulse generators 2, 3 and 4 are identical. The circuit associated with pulse generator 2 is exemplary, and includes two parallel signal paths 7 and 8 connected to the output of pulse generator 2. One path 7 includes a delay device 5. Delay device 5 is provided with a control 6 for varying the delay imparted to a signal passing through the delay device from zero to an amount equal, for example, 'to one-half the period T of the pulses generated by generator 2. The delayed pulse output of delay device 5 is combined with the undelayed pulse in path 8, in combiner 9, which may be for example a twin triode with a common plate load.

The pair of pulses thus derived from each pulse from generator 2 is fed to the input of cathode follower ll.

. It may be seen that by means of control 6 the time spacing of the pulse pair in the output of combiner 9 may be varied smoothly from zero, when the two pulses are coincident, to a value such that the pulses in the output of'combiner 9 are evenly spaced at one-half the period T or twice the frequency of the output of pulse generat or 2. As will be understood more fully hereafter in connection with the description of the receiving portion of the system, the gradual compromise of the precise periodicity of the pulse output of generator 2, which control 6 afiords,,enables a smooth proportional control of the response of the frequency selective element in the receiver which is designed to respond to pulses of period T Variable delay devices 13 and 14, and combiners 1-5 and 16, perform the same functions in association with pulse generators 3 and 4 as do delay device 5 and combiner 9, above described, in association with pulse generator 2. The output of cathode follower 11 therefore consists of the combined pulse outputs, at thedilferent audio frequency repetition rates distinguishing the several respective control channels, of the several pulse generators 2, 3 and 4. This combined modulating signal pulse train is impressed upon the carrier wave output of oscillator 1 and radiated from antenna 9 in a directive pattern to the remote station.

Transmitting antenna 9 may be suitably mounted for movement in azimuth and elevation to enable retention of the remote station receiverin its radiation pattern if the re mote station is for example a mobile vehicle such as an airplane or a ship. Also a receiver may be provided at the control station to recover reflections of the transmitted signals from such a remote vehicle, as in a conventional radio echo ranging system, and thereby assist in tracking the remote vehicle and keeping the transmitting antenna 9 pointed toward it.

Pulse modulation of the carrier has several advantages. By the use of short duty cycle pulses, for example, of the order of one-half microsecond duration, large instantaneous power can be developed from the low average power carrier frequency generators currently known to the art. The high instantaneous power enables a great increase in working range from the control station to the remote station, relative to the range possible with continuous wave modulation. Also the increased frequency spread of the energy in pulse modulation enables a better utilization of the whole radio frequency bandwidth of the transmitter receiver system than can be obtained with continuous wave modulation, thus enabling a relatively improved overall signal-to-noise ratio.

Turning now to Figure 2, there is shown the receiving portion of the system, which it is contemplated will be located at the remote station. A receiving antenna intercepts the transmitted carrier wave signal. This carrier wave signal is amplified in radio frequency amplifier 21, the pulse modulation is recovered by means of a conventional superheterodyne receiver 22, and fed to a video frequency amplifier 23. The combined pulse output of video frequency amplifier 23 consists of the intermixed pulses at the several different recurrence frequencies distinguishing the several different respective control channels, and is in elfect identical with the combined pulse output of cathode follower 11 in the transmitter, Figure l.

.The combined pulse output of the video frequency amplifier 23 is fed if desired to a pulse stretcher 26, which may be for example a one-shot multivibrator, wherein each of the individual pulses is increased in width, and thereby raised in energy level. The train of widened pulses in the output of pulse stretcher 26, representing the combined concurrent control signals for the several control channels, is then fed directly to a control channel selector circuit, wherein pulses at the individual repetition rates distinguishing the particular control channels are selectively recovered. Alternatively the output pulses from pulse stretcher 26 may be fed to the control channel selector circuit through a sine wave forming stage, such as a low pass filter 27, which eliminates all spectral component frequencies in the pulses except the fundamental frequencies corresponding to the difierent pulse repetition rates.

Details of the control channel selector circuit are shown in Figure 3 of the drawings. Filters 41, 42, and 43, Figure 4, are fed in parallel from the output of the pulse stretcher 26. Each of these filters is of the resonant circuit type, as shown in simplified form by the parallel-connected inductance 44 and capacitor 45. Each filter rings, or is resonant, at a particular repetition frequency of the pulses from pulse stretcher 26 and its output will be a maximum at that particular frequency.

The circuits associated with the outputs from the several filters 41, 42 and 43 are" identical in design and operation so that a detailed explanation of the one circuit associated with filter 41 will suffice to explain the operation of all. The output of filter 41 is connected across a potentiometer 61; The sliding contact '62 of potentiometer 61 connects a selected portion of the outputof filter 41 to audio amplifier 63. The plate circuit output of amplifier 63 is in turn rectified by rectifier 64; filtered, and coupled to a direct current amplifier 65. A current-sensitive utilization device 70, which may be for example a solenoid, is energized from the plate circuit of amplifier 65.

In operation, the output of filter 41 will be a sine wave voltage having its highest amplitude when the pulse pairs at the control channel pulse repetition frequency to which the filter 41 is tuned appear in the output of the pulse stretcher 26 with a spacing equal to zero. As the spacing of the pulses is varied from this value the amplitude of the sine wave decreases to a minimum when the spacing is equal to Tl. This alternating current voltage output of filter 41 is suitably attenuated by potentiometer 61, amplified by amplifier 63, and rectified at 64. The positive DC. voltage output which results from rectifier 64 controls the magnitude of the plate current of direct current amplifier 65. This plate current of the amplifier 65 is drawn through the current sensitive utilization device 70 to bring about the desired operation controlled by this channel.

The corresponding portions of the control channel selector stage associated with filters 42 and 43 operate in a manner identical with the operation above described of the circuit associated with filter 41, responsive to the appearance in the output of the pulse stretcher 26 of pulses at the particular control channel distinguishing repetition rate to which the respective filters 42 and 43 are tuned.

The function of potentiometer 61 connected across the output of filter 41, and like potentiometers 71 and 72 connected across the outputs of respective filters 42 and 43, is to enable selective attenuation of the outputs of the several filters. The reason for this is that the output of the filters which are tuned to the highest pulse recurrence frequency will generally be largerthan the outputs of the lower frequency filters, because of the inherently higher energy content resulting from the higher duty factor of the higher repetition rate pulses in the output of the pulse stretcher 26. Thus by appropriate adjustment of the potentiometers 61, 7'1, 72, the outputs of the several filters 41, 42, and 43 can be made equal.

It will be recognized by those skilled in the art that operation of several control channels simultaneously involves the likelihood of destructive interference of control signals due to cross-talk between adjacent channels and between harmonics. The problem has been successfully overcome in the system herein described by purposely avoiding synchronization between the several pulse generators in the transmission portion of the system, and by the further precaution of spacing the pulse repetition rates for the several control channels in a logarithmic manner, so that the spacing of any two adjacent channels is related to their mean frequency by a percentage factor which is constant for all channels. One set of logarithmically spaced pulse repetition frequencies which has enabled successful operation without destructive interference, for example, is: Channel 1, 240 cycles per second; channel 2, 325 cycles per second; channel 3, 440 cycles per second.

Thus there has been shown and described a radio remote control system in which control signals for several channels can be transmitted concurrently on a common carrier wave signal-from a controllstation. to a remote station, by ithelusejofmodulation intelligence signals in the form of low dnty'cycle pulses whose repetition rates distinguish the respective control channels, and in which proportional control. in any one channel is achieved by splitting the pulses distinguishing that channel into pairs, and varying the spacing of the pulses of the pairs.

iThe invention described herein may be manufactured and used :by or for the Government of the United States of America for Governmental purposes without the paymentxof any royalties thereon or therefor. I What is claimed is:

l. A remote control system including a carrier frequency generator, means for modulating said carrier frequency generator simultaneously with pulses at a plurality of different selected repetition rates with adjacent repetition rates being spaced by an amount equal to a constant percentage of memean of said adjacent repetition rates, means for transmitting the modulated carrier frequency signal to a re'mote'statio'n, means at the remote station for demodulating said transmitted signals to recover said modulating pulses, respective frequency selective means for selectively recovering from said modulating pulses the pulses at said respective repetition rates and respective utilization devices operative responsive to the outputs of said respective frequency selective means to control selected operations at said remote station.

2. A multiple channel remote control system comprising control station transmission means including a carrier frequency power oscillator, a plurality of respective pulse generators for generating control intelligence pulses at difierent respective repetition rates, said repetition rates having a spacing such that adjacent repetition rates ditfer by a constant percentage of their mean repetition rate, control means for selectively energizing one or more of said pulse generators concurrently, modulator means fed by the outputs of said plurality of pulse generators for modulating the output of said carrier frequency oscillator with said generated pulses, antenna means for propagating said modulated power oscillator output signals; and remote station receiving means including demodulator means for recovering said pulse modulation, a plurality of respective frequency selective filter means for recovering from said pulse modulation respective pulses having said respective repetition rates, and a plurality of utilization devices fed by the outputs of said respective filter means for controlling selected operations at said remote station.

3. A multichannel remote control system comprising in combination a plurality of pulse group generators for generating pulse groups at different selected group repetition rates corresponding to different respective control channels, means for transmitting said pulse groups to a remote station, receiver means at said remote station for receiving said pulse groups, a plurality of respective frequency selective means fed by said pulse groups for producing respective output signals responsive to pulse groups having said respective selected group repetition rates, means for varying the time spacing of the pulses in the groups generated by any one pulse group generator to vary the amplitude of the output signals from a corresponding one of said frequency selective means, and respective utilization devices fed by the output signals from said frequency selective means for controlling selected operations at said remote station.

4. Apparatus for producing a quantitative response of a controlled function at a remote station proportional in magnitude to the setting of a controlling function at a control station comprising means for producing a controlling signal consisting of groups of pulses having a pulse group recurrence rate distinguishing said controlled function, means for transmitting said controlling signal between said control and remote stations, frequency selective means at said remote station responsive to signals at said pulse recurrence rate for deriving a voltage proportional in amplitude to the precision of recurrence of said controlling signal pulses, voltage magnitude responsive actuating means fed by said derived voltage for varying said controlled function,'and means at said control station for compromising the precision of recurrence of said controlling signal pulses by varying the time spacing of the pulses in each group.

5. A multichannel remote control system comprising transmission means including a carrier frequency generator, means for generating control signal pulses having different repetition rates distinguishing different respective control channels, and modulator means fed by said control signal pulses for concurrently modulating the carrier frequency with said control signal pulses; receiving means including demodulator means for recovering said control signal pulses, respective frequency selective means for deriving respective output voltages proportional to the precision of recurrence of 'said pulses at different respective repetition rates, and respective voltage responsive actuating means fed by said output voltages to control selected respective operations; and proportional control means for varying the degree of response of the actuating means controlled by any one channel including means for variably compromising the precision of recurrence of said control signal pulses generated at said one channel distinguishing repetition rate.

6. A multichannel remote control system comprising transmission means including a carrier frequency generator, means for generating control signal pulses having different repetition rates distinguishing different respective control channels, and modulator means fed by said control signal pulses for modulating the carrier frequency with said control signal pulses; receiving means including demodulator means for recovering said control signal pulses, respective frequency selective means for deriving respective output voltages proportional to the precision of recurrence of said pulses at said different respective repetition rates, and respective voltage responsive actuating means fed by said output voltages to control selected respective operations; and proportional control means for varying the degree of response of the actuating means controlled by any one channel including means for producing from each of the control signal pulses generated at said one channel distinguishing repetition rate a pair of spaced pulses, means for selectively varying the spacing of the pulses of said pair from zero to one-half the period of said one channel distinguishing repetition rate, and means for feeding said spaced pulses to said modulator means in place of said one channel distinguishing control signal pulses.

7. A multichannel remote control system comprising in combination a plurality of pulse generators for generating pulses at different selected repetition rates corresponding to different respective control channels, respective delay means fed by the output of each pulse generator for producing a time spaced image of each generated pulse from said pulse generator, respective combining means fed by the output of its associated delay means and pulse generator for combining each generated pulse and its spaced image to produce spaced pairs of pulses at the repetition rate corresponding to said respective control channel, means for selectively energizing one or more of said pulse generators concurrently, a carrier frequency generator, means for modulating said carrier frequency with the output pulse pairs from said several respective combining means, means for transmitting said modulated carrier frequency signals to a remote station, receiver means at said remote station for recovering said carrier frequency pulse modulation, a plurality of respective frequency selective means fed by said modulation for producing respective output signals responsive to the presence in said modulation of pulses having said respective selected repetition rates, control means in each of said delay means for varying the time spacing of each generated pulse and its image from zero to one-half the period of said generated pulses to vary the amplitude 'ofsaid re' spective output signals irom said frequency selective means, and respective utilization devices fed by the output signals from said frequency selective means for controlling selected operations at said remote station. 7 f 8'. In a remote control system, means for generating a plurality of pulse groups, each of said plurality of pulse groups having a different repetition rate spaced in a selected range such that adjacent repetition rates difier by a constant percentage 'of their mean repetition rate, a signal generator for providing a carrier signal having a desired frequency, means connected between said first mentioned means and said signal generator for simul taneously modulating said carrier signal with said plurality of pulse groups to provide a modulated carrier signal,

' a remote station, means connected to said signal generator for transmitting said modulated carrier signal to saidremote station, a receiver located at said remote station for receiving said modulated carrier signal, a 'plurality'of selective circuits each connected to said receiver and reity of pulse groups to control the amplitude of'thc out-t put signals of the frequency selective circuit responsive to the selected pulse group, and a utilization device connected to each of said plurality of frequency selective circuits and responsive to theoutput signals of the frequency selective circuit for controlling selected operations at said remote stations.

References Cited in the file of patent UNITED STATES PATENTS 2,459,811 Grieg Ian, 25, 1949 2,531,412 Deldraine Nov. 28, 1950 2,594,305 Haller Apr. 29, 1952 2,769,601 Hagopian etal. Nov. 6, 1956 

